Processes for producing light oils and hydrogen from heavy oils have previously been proposed which comprise contacting catalyst particles containing reduced iron with heavy oils and steam in the same fluidized bed reactor at from 500.degree. to 800.degree. C. to crack the heavy oils into light oils and generate hydrogen, burning the coke (carbonaceous component) deposited on the catalyst in a reducing atmosphere to remove it, reducing iron oxide in the catalyst, and recycling the catalyst to bring it again into contact with heavy oils and steam, and an additional step of withdrawing a part of the recycled catalyst and roasting iron sulfide in the catalyst which has been formed during the above reaction. Such is described, e.g., in U.S. Pat. Nos. 4,325,812, 4,421,635 and 4,399,023.
In order to minimize the formation of cracked gases and increase the amount of the light oils obtained by the cracking of heavy oils in the above processes, the temperature of the fluidized bed should preferably be maintained at from 500.degree. to 560.degree. C. However, since the rate of the steam-iron reaction is slow in this temperature range, the temperature of the fluidized bed is preferably maintained at from 600.degree. to 800.degree. C. in order to increase the amount of hydrogen and decrease the volume of the reactor.
The mixing rate of the fluidized particles in the fluidized bed is very high, and the temperature distribution in the bed is nearly uniform. Hence, when the cracking reaction of the heavy oils and the production of hydrogen by the steam-iron reaction are carried out simultaneously at the same temperature in one fluidized bed reactor, the yield of either or both of the light oils and hydrogen must be sacrified.
Furthermore, during the catalytic cracking in the above processes, the reduced iron in the catalyst contacts with sulfur components in the heavy oils to form a large amount of iron sulfide which is unusable to produce hydrogen. Accordingly, the amount of the catalyst which is withdrawn for roasting iron sulfide becomes large, and the reduced iron is wastefully consumed for roasting together with iron sulfide. This is technically and economically undesirable.